1. Field of the Invention
This invention relates in general to a multimedia communications, and more particularly to a method and apparatus for providing resource discovery using multicast scope selection.
2. Description of Related Art
Of the communication tools found in most offices today, such as E-mail, fax machines, pagers, and cellular phones, videoconferencing has yet to make the short list. However, this is changing, as companies move to take advantage of lower system costs and emerging new standards. For example, videoconferencing over an enterprise IP network is very appealing. It makes better use of an organization's funds rather than sinking additional investments in ISDN lines. Up to now, ISDN has been the only reliable way to connect video-enabled workstations and conference-room-based systems. However, the technology isn't readily available, and it's still expensive. Nevertheless, H.323-standard LAN-operable DVC (desktop videoconferencing) solutions are available.
The H.323 standards architecture specifies gateways and gatekeepers that enable connections among LAN-based DVC units, ISDN-connected H.320 units, analog telephone-connected H.324 devices, and ISDN and POTS telephones. One rapidly emerging branch of this market includes gateway and billing server systems devoted to Internet telephony.
The H.323 standard provides a foundation for audio, video, and data communications across IP-based networks, including the Internet. By complying to H.323, multimedia products and applications from multiple vendors can interoperate, thereby allowing users to communicate without concern for compatibility. H.323 will be the keystone for LAN-based products for consumer, business, entertainment, and professional applications.
More specifically, H.323 is an umbrella recommendation from the International Telecommunications Union (ITU) that sets standards for multimedia communications over packet switched networks. This includes Local Area Networks (LANs) that do not provide a guaranteed Quality of Service (QoS), which dominate today's corporate desktops and include packet-switched TCP/IP and IPX over Ethernet, Fast Ethernet and Token Ring network technologies. Therefore, the H.323 standards are important building blocks for a broad new range of collaborative, LAN-based applications for multimedia communications.
The H.323 specification was approved in 1996 by the ITU's Study Group 16. Version 2 was approved in January 1998. The standard is broad in scope and includes both stand-alone devices and embedded personal computer technology as well as point-to-point and multipoint conferences. H.323 also addresses call control, multimedia management, and bandwidth management as well as interfaces between LANs and other networks.
H.323 is the latest of the recommendations on the H.32X series which specifies standards for videoconferencing over a variety of networks. H.323 includes much of the work done since the approval of the H.320 recommendation in 1990, which is a specification for multimedia over circuit switched digital telephone networks. The H.32X is composed of the following recommendations:                H.320 allows videoconferencing over narrowband switched ISDN.        H.321 is for videoconferencing over broadband ISDN ATM LAN.        H.322 allows videoconferencing over Guaranteed bandwidth packet switched networks.        H.323 allows videoconferencing over non-guaranteed bandwidth packet switched networks.        H.324 is for videoconferencing over PSTN or POTS (the analog phone system).        
The H.323 Protocol Stack supports many real time applications that the industry is eager to use through the Internet such as: Desktop Videoconferencing, Internet Telephony and Videotelephony, Collaborative Computing, Business Conference Calling, Distance Learning, Support and Help Desk Applications, etc. These applications already exist in the market, but most of them do not address the problem of how to run these applications over a packet switched network like the Internet and most corporate LANs which are based on the TCP/IP suite of protocols. With the pressure of the market to use these kinds of applications over the Internet, H.323 emerges as a possible solution to the business needs.
H.323 defines four major components for a network-based communications system. FIG. 1 illustrates a H.323 system 100. In FIG. 1, the four major components of a H.323 system 100 are shown including their interaction with existing networks. These components interact with LANs that may not provide QoS. The four components include Terminals 110, Gateways 120, Gatekeepers 130 and Multipoint Control Units (MCUs) 140.
These four elements 110-140 are specified only for the Application Layer of the Internet Layer Model. There is no specification about the lower layers (Transport, Network, Data link and physical layers). This characteristic makes H.323 flexible and allows H.323 devices to communicate with devices of other networks.
H.323 Terminals 110 are the client software that runs in the end user computers that allow users to communicate in real time using all the power of multimedia. These terminals are also called Endpoints.
A Gateway 120 is a component of the H.323 specification that provides world wide connectivity and interoperability from LAN. That is, a Gateway 120 will allow computers connected to a LAN to communicate to regular phones 150 connected to the PSTN 152, to digital phones 154 (H.320 terminals) connected to an ISDN network 156. A gateway 120 also translates between different types of codecs used by different kinds of terminals, maps call signaling between Q.931 to H.225 and maps control signaling between H.242/H.243 to H.245.
In general, a Gateway 120 is a component that makes possible to interconnect a packet switched network to other types of networks. If connections to different types of networks are not required, then a Gateway 120 is not required since terminals can communicate between them if they are on the same LAN. Terminals communicate with gateways using H.225.0 and H.245 protocols.
A Gatekeeper 130 is an H.323 component that performs four basic functions:                Address Translation: It is the mechanism that allows to have different kinds addressing systems. For example, regular phone numbers (E.164 addresses) can be used in conjunction with email addresses. The Gatekeeper 130 allows to communicate with terminals addressed in different ways.        Admission Control: The Gatekeeper 130 could reject calls from users. An user must be registered with the Gatekeeper 130 in order to complete a call.        Bandwidth Control: Networks managers can restrict the amount of bandwidth used for videoconference, which provide a way to control LAN traffic. The remaining of the bandwidth can be used then for web requests, email, file transfers, etc.        Zone Management: The Gatekeepers 130 provide the functions of Address Translation, Admission Control and Bandwidth control for Terminals 110, MCUs 140 and Gateways 120 registered with the Gatekeeper 130 in its zone of control. This zone is called H.323 zone.        
The functions of the Gatekeeper 130 are included in the Gateway 120 by most vendors, although they are logically separate and they perform different kinds of functions.
The Multipoint Control Unit (MCU) 140 is a logical device that supports conferences between two or more endpoints. The MCU 140 typically is integrated with the implementation of the gateway, so in most implementations the MCU 140 won't be a separate computer performing conferencing functions. Also, with a combined implementation of the functions of the MCU 140 with the functions of the gateway 120, conferences among participants of different networks (LAN and PSTN) will have better performance than divided implementations.
In operation, several applications need to discover resources of different kinds depending on different criteria. For instance, in the H.323 standard, a Terminal 110 may need to discover a suitable Gatekeeper 130 so that it may register with it. Such resource discovery needs to occur in a dynamic fashion to account for possible topology changes and failures within the network. Moreover, the mechanism needs to be simple and efficient.
It can be seen then that there is a need for an efficient way of implementing the method of multicasting to a well-known group of resources when dynamic resource discovery is warranted.
It can also be seen that there is a need for a method and apparatus for providing resource discovery using multicast scope selection.